1. Field of the Invention
The present invention relates to a culture vessel, and a microscope for observing the sample in the culture vessel.
2. Description of the Related Art
A culture vessel manufactured by disposing a plurality of culture ponds (referred to a well hereinafter) with well-like shapes or concave shapes on a plate (referred to a well plate hereinafter) for cell culture has been known in the art. While a variety of inner diameters of the well are available, the number of the wells disposed on the well plate increases as the inner diameter of the well becomes smaller. A well plate on which wells with an inner diameter of 16.5 mm or less, or 24 or more of the wells, are disposed is practically used (for example, the Multi-well Plate 3047 and Micro-test Plate 3070 made by Becton Dikinson Co. have 24 wells and 96 wells, respectively).
However, the range where a phase contrast effect is obtainable is limited to a central portion of the well when one attempts to observe the cells cultured on a well plate having many wells with a small inner diameter, because the liquid surface of the culture medium in each well is curved due to surface tension of the liquid surface. It is needless to say that this tendency becomes evident as the inner diameter of the well becomes smaller, or the number of the wells becomes larger, being extremely evident in the well plate on which 96 wells are disposed.
The inventor of the present invention has disclosed a method (referred to a related method hereinafter) for solving the foregoing problems in J. P. Preliminary Publication No. Hei 8-5929. In the basic construction of the related method, an attachable and detachable lens system having a positive refractive power is placed between the condenser lens disposed in the illumination optical system of the microscope and well plate as described above so as to cancel the negative refractive power generated by surface tension of the culture medium, thereby spreading the available range for obtaining the phase contrast effect to enable a comfortable phase contrast observation with the microscope.
Although the related example described above is basically worth evaluating, a favorable construction for responding to various conditions should be considered for turning the method to practical uses. One of the conditions to be considered will be described referring to FIG. 1 and FIG. 2. FIG. 1 illustrates the construction in the related example while FIG. 2 is provided for describing the problems in the related example. In FIG. 1, the reference numeral 1 denotes a ring-shaped opening (a diaphragm) disposed in the illumination optical system, the reference numeral 2 denotes a condenser lens, and the reference numeral 3 denotes an attachable and detachable lens system having a positive refractive power placed in the optical path of the illumination optical system. However, the lens system 3 is not necessarily composed of one lens element. The reference numeral 4 denotes a well plate on which a number of wells 5 are disposed. A cultivation medium 6 is filled in each well 5. The reference numerals 7 and 8 correspond to an objective lens and a phase contrast plate, respectively, while the reference numeral 8a denotes a phase contrast membrane.
The construction as described above enables a phase correction when the center line 5-0 of the inner diameter of the well 5 is exactly or nearly exactly aligned with the optical axis 3-0 of the lens system 3. However, when the center line 5-0 of the inner diameter of the well 5 is not aligned with the optical axis 3-0 of the lens system 3 but the lines are considerably separated with each other, a sufficient phase correction becomes difficult.
When the lens system 3 is attached to fix its optical axis to the optical axis of the illumination optical system with a construction not to allow the lens 3 (and its optical axis 3-0) to move in the related example, the center line 5-0 of the well can not be aligned with the optical axis 3-0 of the lens system 3 when the well plate 4 is allowed to move for observing the peripheral region of the well. Consequently, a sufficient phase correction becomes impossible thus making observation of the peripheral region difficult. When the optical axis of the lens system 3 is not fixed to the optical axis of the illumination optical system, on the other hand, the lens system 3 should be moved independently from the movement of the well plate 4 for every wells for successively observing different plural respective wells 5, requiring a considerable time for the movement as well as poor working performance.
Moreover, both of the projection position and projection magnification of the ring-shaped opening are simultaneously corrected by using two or more of lenses for the purpose of expanding the area where a phase contrast effect is obtainable in the related example, using two or more of lenses as described above renders a relatively high production cost as compared with the case that uses single lens with a positive refraction power.